Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing a new design; and

FIG. 2 is a front view of a second embodiment thereof; and,

FIG. 3 is a front view of a third embodiment thereof.

The outermost box in broken lines in the Figures illustrates the perimeters of a display screen or portion thereof and forms no part of the claimed design.

Subject matters in broken lines in the Figures, such as text boxes, texts, words, letters, symbols, icons, numbers, images, and/or lines, form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 